Nova Southeastern University NSUWorks Theses and Dissertations HCNSO Student Work 11-1-2013 Characterization of Shark Movements on a Mesophotic Caribbean Coral Reef and Temporal Association with Fish Spawning Aggregations Alexandra E. Pickard Nova Southeastern University Oceanographic Center, [email protected] This document is a product of extensive research conducted at the Nova Southeastern University Halmos College of Natural Sciences and Oceanography. For more information on research and degree programs at the NSU Halmos College of Natural Sciences and Oceanography, please click here. Follow this and additional works at: http://nsuworks.nova.edu/occ_stuetd Part of the Marine Biology Commons Share Feedback About This Item NSUWorks Citation Alexandra E. Pickard. 2013. Characterization of Shark Movements on a Mesophotic Caribbean Coral Reef and Temporal Association with Fish Spawning Aggregations. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, Oceanographic Center. (11) http://nsuworks.nova.edu/occ_stuetd/11. This Thesis is brought to you by the HCNSO Student Work at NSUWorks. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of NSUWorks. For more information, please contact [email protected]. NOVA SOUTHEASTERN UNIVERSITY OCEANORAPHIC CENTER CHARACTERIZATION OF SHARK MOVEMENTS ON A MESOPHOTIC CARIBBEAN CORAL REEF AND TEMPORAL ASSOCIATION WITH FISH SPAWNING AGGREGATIONS By Alexandria Elizabeth Pickard Submitted to the Faculty of Nova Southeastern University Oceanographic Center in partial fulfillment of the requirements for the degree of Master of Science with a specialty in: Marine Biology Nova Southeastern University November 2013 Table of Contents Acknowledgements _________________________________________ 3 Abstract __________________________________________________ 4 Introduction _______________________________________________ 6 Materials and methods _______________________________________8 Study site ____________________________________________ 8 Sampling ____________________________________________ 8 Acoustic monitoring ____________________________________9 Analysis ____________________________________________ 10 Results __________________________________________________ 14 Mesophotic reef use ___________________________________14 Association of sharks with the fish spawning aggregation site__ 16 Discussion _______________________________________________ 19 Mesophotic reef use___________________________________ 19 Association of sharks with the fish spawning aggregation site__ 21 Conclusions ______________________________________________ 25 Tables and figures _________________________________________ 27 Appendix ________________________________________________ 34 Literature cited ___________________________________________117 2 Acknowledgements Thank you to my committee members: Dr. Mahmood Shivji, Dr. Brad Wetherbee, and Dr. Jeremy Vaudo. It has been an honor and a valuable experience working with all of you. You have taught me a great deal about sharks, research, writing, and life over the past two years. The completion of this project would not have been possible without your direction and expertise. Dr. Hardigan, you have been instrumental in the completion of my statistical analyses. I greatly appreciate the time you offered and the interest you showed in my study. Thank you to Nova Southeastern University Oceanographic Center for providing me the opportunity to pursue this degree at a world-class institution under the guidance of faculty who are at the forefront in their fields of research. On a personal note, I acknowledge my fellow labmates: Andrea Bernard, Kimberly Atwater, Shara Teter, Teagen Gray, Christine Testerman, and Derek Burkholder for all of your encouragement, scientific guidance, and friendship. Your company and antics made coming to the lab something I looked forward to. I would be remiss if I did not thank my family, particularly my parents, who have fostered my passion for marine biology from a young age, by chartering a boat throughout the US and British Virgin Islands every February. It is there where I developed my interest in the ocean, and fortuitously, conducted my thesis research. Thank you to my Mom and Dad for also providing immense emotional and financial support throughout my entire academic career, and most recently while earning my masters degree. This research was funded by the operational funds to the Guy Harvey Research Institute at Nova Southeastern University’s Oceanographic Center. Thank you Dr. Harvey for your generosity and lifelong dedication to ocean conservation. 3 Abstract Habitat use of mesophotic coral reefs by sharks is largely unknown. However, it is well established that mesophotic reefs are the site of spawning aggregations for many species of teleost fish. These aggregations represent seasonal concentrations of potential prey biomass that may influence the habitat use of predatory species such as large sharks. I employed acoustic monitoring to examine the movements of three shark species [lemon shark (Negaprion brevirostris), tiger shark (Galeocerdo cuvier), and Caribbean reef shark (Carcharhinus perezi)] to determine 1) the comparative spatiotemporal patterns of mesophotic reef habitat use by the three shark species and 2) the spatiotemporal relationship between these sharks and grouper spawning aggregations at a fish spawning aggregation (FSA) site (Hind Bank and Grammanik Bank) along the southern reef shelf edge off St. Thomas, United States Virgin Islands (USVI). Tiger and lemon sharks were detected across nearly the entire acoustic array, which spanned ~ 1060 km2. When present, Caribbean reef sharks used a much smaller activity space, composed exclusively of mesophotic reef habitat located within FSA sites. Individuals from all three species were typically detected for stretches of several consecutive days, while periods without detections usually lasted less than one week. Lemon sharks were present at the FSA site more often during the grouper spawning season (Dec-May) than the non-spawning season (Jun-Nov), but showed no preference toward specific areas within the FSA site, which varied by location and grouper species composition. In contrast, there was no relationship between the presence of tiger and Caribbean reef sharks at the FSA site and the grouper spawning season. My results suggest that despite different habitat use 4 patterns and varying degrees of fidelity, this mesophotic reef serves as an important habitat to all three shark species. Keywords: lemon shark, tiger shark, Caribbean reef shark, grouper, acoustic telemetry, habitat use, US Virgin Islands, Puerto Rico 5 Introduction Mesophotic reefs, which have been loosely defined as ranging in depth from 30 m to depths where light levels are too low for coral phototrophic symbionts to sustain coral growth via photosynthesis [1], may make up a considerable amount of available reef habitat. Although mapping of mesophotic coral reef ecosystems is in its infancy, more than 186,000 km2 of potential mesophotic coral habitat has been identified in U.S. waters alone [2]. However, because of technological limitations and safety issues associated with working near or below the depth limits of SCUBA diving, studies on mesophotic reef ecology have lagged greatly behind studies on shallow reefs [3-5]. Large sharks are upper level predators [6] and likely play an important structural role in marine ecosystems [7,8], including coral reef systems [9,10]. Because movement patterns determine the spatial and temporal extent of species interactions, understanding the movements and habitat use of these predators is a necessary step to determining their role in ecosystems. Although shark movements and habitat use have been studied in several shallow coral reef systems [11-14], little is known about how sharks use mesophotic reefs. Given the large amount of mesophotic reef habitat that exists and that worldwide many shark populations are declining [15,16], studies of shark movements on mesophotic reefs are of increased importance. There are many factors that can affect movements and habitat use of mesophotic reefs by sharks. One such factor that can vary spatially and temporally is prey distribution. Fishes are an important component of the diets of many sharks [6], 6 and mesophotic reefs are important habitats for many fishes, particularly during spawning. These spawning fishes seasonally form large fish spawning aggregations (FSAs) [17]. FSAs can be composed of hundreds to thousands of individuals and are highly predictable in both timing and location [17]. Such large and predictable prey aggregations have been known to attract shark species [11,18,19] and may similarly influence shark movements on mesophotic reefs. The insular slope reefs of Puerto Rico and the United States Virgin Islands (USVI) are located predominantly at mesophotic depths (i.e., 30 – 100 m) [20] and are an ideal location to examine the movements of sharks, which occur in high densities in this area, on mesophotic reefs [21]. These reefs are also relatively undisturbed by anthropogenic influences because of the reef’s considerable distance from land, runoff and other pollutants [20,22]. In addition, several well-studied FSAs are found on the mesophotic reefs south of St. Thomas, USVI, allowing for examination of the association of sharks and FSAs. Here I describe the mesophotic reef use of three shark species along the Puerto Rico-Virgin Islands platform using passive acoustic